Conventionally, there has been known a soot detecting device that detects particulate matter that is generated in an internal combustion engine or the like, more specifically, soot composed of carbon, as is disclosed in Japanese Patent Laid-Open No. 2009-281974, for example. The particulate matter is also abbreviated as “PM” in general. The soot detecting device according to the publication includes an oxygen ion conductor such as stabilized zirconia, heating means that heats an oxygen ion conductor, a first oxygen concentration measuring section that measures an oxygen concentration which is changed by combustion of soot.
The temperature of the oxygen ion conductor is controlled to the temperature at which soot remains and combustion of the soot is enabled by oxygen (active oxygen) that is supplied by pumping. At a time of detection of soot, a voltage is applied to between both electrodes at the oxygen ion conductor to perform pumping of oxygen, and by using the pumped oxygen, soot is combusted at the controlled temperature. Since the first oxygen concentration measuring section issues an output (a current value, for example) indicating an oxygen concentration, detection of soot (calculation of the amount of soot or the like) can be performed by using the output. However, the above described conventional art performs oxygen pumping by applying a voltage to between both the electrodes at the oxygen ion conductor while keeping the control temperature in a fixed range, and does not change the control temperature intentionally.